1. Field of the Invention
The present invention relates to pattern forming methods, and, particularly, to a method for forming a pattern by photo-nanoimprinting.
2. Description of the Related Art
A photo-nanoimprinting method is a technique for forming projections and recesses in a resin thin film on a substrate by curing the resin thin film while a mold having a surface provided with projections and recesses is pressed against the resin thin film, and thus transferring the projections and recesses to the thin film. The mold may be referred to as a stamper.
In the photo-nanoimprinting method, the mold and the cured resin thin film adhere to each other, and a high releasing power is required for separating them from each other. However, high releasing power may cause a defect such as a crack in the pattern of the cured film, or cause the substrate having the cured film to rise from the surface of a stage on which the substrate has been placed and result in a reduced precision in alignment. Accordingly, it is desirable to reduce the releasing power.
Japanese Patent Laid-Open No. 2010-262980 teaches that a gas generator agent is added to a curable composition for nanoimprinting lithography.
Japanese Patent Laid-Open No. 2010-103464 discloses an imprinting method using a photo-curable resin that can generate a gas in at least either a heating condition or a pressuring or pressure-reducing condition (paragraph 0118). In this method, a mold is brought into contact with a photo-curable resin in a high pressure atmosphere and, then, irradiating the photo-curable resin with light through a mold to cure the photo-curable resin. Then, the high pressure atmosphere is changed into a reduced pressure atmosphere, so that the gas contained in the cured film of the photo-curable resin is evaporated and accumulated in the boundary between the cured film and the mold. The gas accumulated in the boundary lowers the adhesion between the cured film and the mold.
The gas generator agent described in Japanese Patent Laid-Open No. 2010-262980, which is allowed to generate a gas by light or heat, undesirably generates a gas when the curable composition is cured by light. This can generate bubbles while the curable composition is cured, and result in transfer failure.
In the method described in Japanese Patent Laid-Open No. 2010-103464, a gas is generated within the photo-curable composition by pressure application and pressure reduction. Accordingly, a chamber for performing pressure application and pressure reduction is used, and the process of the method requires a lot of time and effort.